Enterococci are bacteria that grow naturally inside human intestines. Over the last few decades, these pathogens have developed resistance to our most potent antibiotics, including vancomycin, an antibiotic of last resort for infectious disease. Vancomycin-resistant Enterococcus (VRE) does not cause illness to healthy individuals. But it does cause severe illness to hospital patients, especially the ones who have undergone antibiotic therapy. Antibiotic therapy eliminates a lot of the good bacteria in the gut of humans. VRE grab and fill this vacuum, spreading quickly from the intestines to the bloodstream and from there to the spleen, the liver, the heart. There they grow and cause disease that can no longer be easily treated with antibiotics. We genetically engineer lactic acid bacteria (LAB) to specifically target enterococcus inside gastrointestinal (GI) tracts. We propose to administer these cellbots to mice and examine if enterococcus vanishes from mouse GI tracts. We pursue three specific aims: First we engineer smart LAB that can detect enterococci. Upon detection, engineered LAB produce and release proteins. In the second aim, we engineer these proteins to be lethal to enterococci. In the third aim, we will examine the efficacy of our modified LAB in mice. We will infect mice with enterococcus and then administer LAB to them. The main hypothesis is that engineered LAB kill enterococci and stop their colonization inside animal GI tracts. If successful, these experiments can lead to the development of a promising therapeutic strategy against enterococcal infections.